From what I have read in the PHB the benefits of the Great Weapon Fighting fighting style apply to both two-handed (heavy) weapons and using a versatile weapon with two hands.

The Great Weapon Master feat (PHB p. 167) says that the -5/+10 can only be used with heavy weapons. That means gnomes and halflings, or any Small or otherwise character who can can use versatile weapons but can only wield Heavy Weapons at disadvantage (an effective -5) have an increased penalty from this part of the feat.

Were versatile weapons left out of the Great Weapon Master feat for
thematic/flavor reason, or are there mechanics, skills, or abilities
that can "break" the game?

\$\begingroup\$Are you asking why the designers chose to make it like this, or whether it has been changed?\$\endgroup\$
– kviiriMay 23 '17 at 8:42

\$\begingroup\$I would like to know why was chosen like that and if house ruling it would break anything.\$\endgroup\$
– DavidMay 23 '17 at 10:16

1

\$\begingroup\$Asking about designer intent is a bit thorny here: it requires people to find explicit designer statements to back up the assertion, which is a potentially extraordinary task -- or impossible if such statements don't exist -- that I suspect is tangential to your issue.\$\endgroup\$
– doppelgreener♦May 23 '17 at 15:51

2

\$\begingroup\$Small creatures CAN use Heavy Weapons - they just do so at disadvantage. You may want to clarify your question.\$\endgroup\$
– NautArchMay 23 '17 at 16:44

1 Answer
1

Versatile weapons cannot work with this feat.

You’ve learned to put the weight of a weapon to your
advantage, letting its momentum empower your strikes.

Rules-wise, the definition is perfectly clear.

Before you make a melee attack with a heavy weapon
that you are proficient with, you can choose to take a
-5 penalty to the attack roll. If the attack hits, you add
+10 to the attack's damage.

The feat is targeted at only STR-based characters, using both hands (as all Heavy weapons have the two-handed property). It is too flexible to be used with versatile weapons. Consider that you could drop something from your hand (like an Arcane Focus, or something else), attack with both hands, and pick the thing back up with your free-object interaction. This is even more imbalanced when characters have multiple attacks, advantage, and/or extra turns or abilities.

Eldritch Fighters could use their Action Surge to either attack several more times and re-equip the Arcane Focus for a War Caster AoO.

Multi-classing into Rogue-3 makes you able to use Fast Hands to equip a shield as a bonus action, so allowing you to have +2 Armor when your turn was done.

But maybe the most broken combo here would be Monks. Dexterity monks could now use a 2-handed DEX Quarterstaff with -5/+10 along with their unarmed strikes.

Any character with Haste (+2 AC, and an additional action)

I'm sure there are other cheesey combos out there that could be abused.

Consider also that you could now use this with weapons like the Quarterstaff, Trident, or Spear, which only do 1d8 damage (when used with both hands). Getting a +10 damage on a weapon whose maximum damage is 8 is a lot more valuable than with a weapon whose maximum damage is 10 to 12.

As a house-rule, I would not allow it. I very much enjoy the flavor, and the limitation, of the feat, requiring a big and heavy weapon to be used. My players are also power-gamers - I'm sure they'd exploit this somehow. When fighters and barbarians can pull off several attacks per turn with advantage, this becomes quite imbalanced compared with casters or ranged characters.